The present invention relates to a new and improved construction of transformer for the controllable shifting of the phase angle of the output voltages in relation to the input voltages, especially for an alternating-current voltage compound network, containing at least one secondary winding galvanically decoupled from the primary winding and subdivided into stages or sections.
When coupling together a number of energy transmission lines attempts are made to ensure that the phase angles of the coupled alternating-current voltages are in-phase. Consequently, there is improved the transmission characteristics of the line and there is avoided any spill back at the generators. This desire is made more difficult because the phase angle of a voltage infed to a transmission line is shifted along the line and by the load at the end of the line, if such load is not a pure active resistance.
In the case of compound networks there are preferably employed shunt transformers in order to accommodate the phase angle of the voltages in the different network sections. The shunt transformer induces in each conductor of the line a shunt voltage superimposed upon the input voltage, and the phase angle of which, in relation to the phase angle of the input voltage, is shifted by 90.degree., so that there appears an output voltage whose phase angle is shifted in relation to the phase angle of the input voltage. Usually, the winding provided for generating the shunt voltage is divided into a number of stages, so that there can be tapped-off shunt voltages having different amplitudes. This renders it possible to shift the shunt output voltage throughout different angular ranges. Shunt transformers only render possible a stepwise shifting of the angle of the output voltage in one direction and through relatively small regions and require for changing the tapping at the shunt voltage winding technically complicated and relatively sluggish mechanical switches.
Hence, there has already been proposed a controllable phase shifter which can be employed in lieu of a shunt transformer, for the direct connection of two transmission lines or for generating the additional voltage or potential for a shunt transformer. This phase shifter contains at least two reactive impedances connected in series, between which there is provided a tap, and connected in series with at least one of these impedances is an electrically controlled current switch, preferably a bidirectional thyristor. This phase shifter can be connected directly between two phases of the transmission line or the secondary windings of a transformer. Such phase shifter renders possible a practically continuous shifting of the phase angle of the tapped-off voltage in each of both possible directions. The current switch of the phase shifter can be connected with an electronic control circuit, rendering possible a practically undelayed optimum alignment of the phase angle of the delivered potential. With this phase shifter the shifting of the phase angle is accomplished by the reactive or blind load in the reactive impedances, accounting for the reason why the magnitude of the phase shift determines the requisite rated load of the impedances. The rated load amounts to approximately one-quarter of the power rating or power-handling capacity for a phase shift through 60.degree.. The described phase shifter, notwithstanding its technological advantages, therefore for purely economical reasons is only useful to a limited extent for energy transmission lines.